import java.util.Scanner;
/**
 * Created with IntelliJ IDEA
 * Description:
 * User: Administrator
 * Data: 2023 - 09 - 30
 * Time: 11:21
 */
//牛客 不要二
public class Solution12 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int w = in.nextInt();
            int h = in.nextInt();
            int[][] arr = new int[w][h];
            int count = 0;
            for (int i = 0; i < w; i++) {
                for (int j = 0; j < h; j++) {
                    if(arr[i][j] == 0) {
                        count++;
                        if(j + 2 < h) arr[i][j + 2] = 1;
                        if(i + 2 < w) arr[i + 2][j] = 1;
                    }
                }
            }
            System.out.println(count);
        }
    }
}
